The present invention relates to a goniometric device particularly for X-ray or neutron diffractometry on monocrystals or any other sample.
Diffractometers known at the present time for the study of monocrystals by X-ray analysis, are of the "four circles" or derived type and they allow the displacement of the monocrystal in rotation about three axes concurrent at the same point. This monocrystal is generally mounted on a sample-holder mobile in rotation about a first axis, of angle .phi., this sample-holder is in turn mounted on an inner circle itself mounted to rotate inside an outer circle, about a second axis perpendicular to the first, of angle .chi., and finally the outer circle is mounted to rotate about a third vertical axis which is the axis of the goniometer, the outer circle rotating about this third axis of angle .omega.. Although generally suitable for studying monocrystals in the open air, such diffractometers are not adapted to the study of the properties of these monocrystals housed inside a tight enclosure.
It is an object of the present invention to remedy these drawbacks by providing a device for making the measurement on monocrystals or other sample placed inside a tight enclosure, with very high precision, in the lack of any control goniometer.
To this end, this goniometric device particularly for X-ray or neutron diffractometry on monocrystals or any other sample comprising a sample-holder to maintain the monocrystal to be analyzed in the axis of the incident X-ray or neutron beam, means for driving this sample-holder on itself, about a first axis, and also in rotation about a second axis perpendicular to the first and a third axis perpendicular to the second, is characterized in that the sample-holder is borne by a slave-goniometer comprising a transverse bar made of ferromagnetic material fast with the sample-holder, therefore perpendicular to the first axis of rotation of the sample-holder on itself, a support on which the sample-holder is rotatably mounted and which forms part of a universal joint mounted on a fixed base and of which the two perpendicular axes correspond respectively to the second and third axes of rotation, and means are provided for creating a magnetic field whose orientation varies in space so that, for each determined orientation of the magnetic field, the ferromagnetic bar and consequently the sample-holder and the monocrystal take this same orientation. Perpendicular is understood to mean that fact that two axes form together an angle of 90.degree. or slightly different.
The means creating the magnetic field whose orientation varies in space may be constituted by a permanent magnet mounted to rotate on itself about the first axis and which replaces the conventional goniometric head.
According to a variant embodiment of the invention, the means creating the magnetic field with space-variable orientation are constituted by an assembly of coils disposed around the slave-goniometer and having currents of adjustable intensities passing therethrough, the elementary magnetic fields created by the different coils contributing to form a resultant magnetic field of variable orientation which controls the positon of the sample-holder.
The goniometric device according to the invention offers the advantage that, due to the use of a magnetic coupling for obtaining servo-control of the position of the sample-holder, it is possible to isolate the sample-holder and the monocrystal subjected to the study from the outside by means of a tight enclosure. It is thus possible to make measurements at very low temperatures, by housing the slave-goniometer inside a cryostat. Measurements may also by made in a gaseous environment other than air, in an enclosure with controlled hygrometric degree or in which a pressure prevails which differs from atmospheric pressure (vacuum or pressure of several tens of bars).
Thanks to a judicious choice of the materials constituting the goniometric device and of the pivots chosen to allow the movements of rotation, it is possible to obtain, with the goniometric device, a precision of positioning of the order of 0.005.degree..